This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-266246, filed Sep. 3, 2001, the entire content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an image-recording apparatus which ejects ink to a recording-medium and records an image.
2. Description of the Related Art
Image-recording apparatuses such as an ink jet printer, ejects ink to recording media such as paper and a records an image. The image-recording apparatus comprises a recording-head for discharging ink to the recording-medium; a carriage for holding the recording-head; conveying means for conveying the recording-medium; and carriage-driving mechanism for moving the recording-head in a direction (main scanning direction) crossing at right angles to a conveying direction (sub scanning direction) of the recording-medium by the conveying means.
In the image-recording apparatus, the carriage is driven along the main scanning direction. When the carriage is driven, the recording-head is moved along the main scanning direction. During the movement, the recording-head ejects ink drops to the recording-medium. Thereby, the image-recording apparatus puts the ink drops to the recording-medium at substantially constant pitches along the main scanning direction. Thereby, the image-recording apparatus records an image corresponding to a width of the recording-head in the recording-medium. The image-recording apparatus repeats the above-described recording on the recording-medium intermittent conveyed along the sub scanning direction. The image-recording apparatus repeats the recording to record the whole image in the recording-medium.
A conventional image-recording apparatus will be described hereinafter. FIG. 12 is a side view showing the conventional image-recording apparatus. In the image-recording apparatus, as shown in FIG. 12, carriage-driving mechanism 110 includes a pair of pulleys 111, endless belt 112, motor 113, and carriage support portion 114. Moreover, the carriage is denoted with a reference numeral 120 in FIG. 12. The carriage 120 has a recording-head. Additionally, in FIG. 12, the sub scanning direction is a direction extending along an arrow AS. The main scanning direction extends along an arrow AM.
A pair of pulleys 111 are disposed apart from each other along the main scanning direction. An image-recording area ZP and two reverse areas ZR are disposed between the pair of pulleys 111. The image is recorded to a recording-medium 200 in the image-recording area ZP. A width of the image-recording area ZP along the main scanning direction is set to be substantially the same as or slightly larger than the width of the recording-medium 200. In the reverse areas ZR, the movement direction of the carriage 120 moved along the main scanning direction is reversed. The reverse areas ZR will be described in more detail. The carriage 120 moves in the image-recording area ZP. When the carriage 120 moves beyond the image-recording area ZP, the carriage 120 changes its moving-direction (turns about) toward the image-recording area ZP again. That is, the carriage changes its moving-direction in the reverse areas ZR. Therefore, the reverse areas ZR are disposed near the respective pulleys 111. In other words, the reverse areas ZR are disposed on the opposite sides via the image-recording area ZP between the pair of pulleys 111.
The endless belt 112 is supported by the pair of pulleys 111.
The motor 113 is connected to one of the pair of pulleys 111. The motor 113 supplies its driving force to the pulleys 111.
The carriage support portion 114 is fixed to the endless belt 112, and supports the carriage 120. That is, the carriage 120 is fixed to the endless belt 112 via the carriage support portion 114.
The carriage-driving mechanism 110 is driven by the motor 113 to operate the endless belt 112 supported by the pulleys 111. The carriage 120 can be reciprocated along the main scanning direction by the action of the endless belt 112. Therefore, the carriage-driving mechanism 110 can reciprocate the recording-head fixed to the carriage 120 along the main scanning direction.
There is an image-recording apparatus of a reciprocating print type. The reciprocating print type is an image recording system for discharging ink in both forward and backward movements during the reciprocating movement of the recording-head, and recording the image. Moreover, the image-recording apparatus has various types of arrangement of the recording-head. For example, as described in Jpn. Pat. Appln. KOKAI Publication No. 1998-250058, there is also an image-recording apparatus in which a plurality of recording-heads are arranged along the main scanning direction.
In the above-described image-recording apparatus, while the recording-head is moved, the ink is ejected. Therefore, in the image-recording apparatus, in order to record a high-quality image, it is preferable to move the recording-heads constantly at a constant speed in the image-recording area ZP. For this, the carriage-driving mechanism 110 needs to include the pulleys 111 and motor 113 which completely have no eccentricity. That is, the carriage-driving mechanism 110 in an ideal state includes the pulleys 111 and motor 113 which completely have no eccentricity. However, in the actual carriage-driving mechanism 110, it is very difficult to completely remove the eccentricity of the pulleys 111 and motor 113.
Additionally, an action of the image-recording apparatus including the carriage-driving mechanism 110 in the ideal state will be described hereinafter with reference to FIG. 13. FIG. 13 is a diagram showing shot positions that the ink drops ejected in the above-described ideal state take on the recording-medium 200. Additionally, FIG. 13 is a schematic enlarged top plan view showing the operating recording-heads of the image-recording apparatus of FIG. 12. Additionally, in the following description, a case in which the image-recording apparatus records the image in the reciprocating print mode, particularly one path reciprocating print mode.
In FIG. 13, a reference character Vf denotes a set movement speed in the forward movement of the recording-head 130, and reference character Vr denotes the set movement speed in the backward movement of the recording-head 130. Additionally, the set movement speeds Vf, Vr in the forward and backward movements are set to be the same in order to move the carriage 120 at the constant speed. Furthermore, in the image-recording apparatus, the carriage-driving mechanism 110 in the ideal state drives the recording-head 130 via the carriage 120. As a result, the speed of the recording-head 130 in the reciprocating movement is constantly the same as the set movement speeds Vf, Vr.
First, the action of the recording-head 130 which moves in the forward movement will be described.
The recording-head 130 in FIG. 13 is moved by the carriage-driving mechanism 110 along the main scanning direction in the ideal state. Therefore, the recording-head 130 moves at the set movement speed Vf as set along the main scanning direction.
The recording-head 130 is apart from the recording-medium 200 by a distance Dg. Therefore, a time t obtained by the following equation 1 is required from when the ink drops are ejected from the recording-head 130 until the ink drops are shot on the recording-medium 200.
t=Dg/Vixe2x80x83xe2x80x83Equation 1 
Where Vi is a eject speed of ink
Subsequently, in the forward movement, the ink drops are ejected from the recording-head 130 which is moving at the speed Vf, and therefore deviate from ejecting positions toward a forward direction of the recording-head 130. Therefore, in the forward movement the ink drops ejected from the recording-head 130 have shot positions which deviate from the eject positions by a distance Df obtained by the following equation.
Df=Vfxc3x97txe2x80x83xe2x80x83Equation 2 
The action of the recording-head 130 during the backward movement will next be described.
The recording-head 130 in FIG. 13 is moved by the carriage-driving mechanism 110 in the ideal state, and therefore moves at the set movement speed Vf as set. Also during the backward movement, the recording-head 130 ejects the ink drops at a eject speed similar to that of the forward movement. Therefore, similarly as the forward movement, a time required until the ink drops are shot on the recording-medium 200 is time t.
Moreover, during the backward movement, the ink drops are ejected from the recording-head 130 moving at the set movement speed Vr. Therefore the ink drops deviate from the eject positions toward the moving-direction of the recording-head 130. Therefore, in the forward movement, the ink drops is struck at the shot positions which deviate from the eject positions by a distance Dr obtained by the following equation 3.
Dr=Vrxc3x97txe2x80x83xe2x80x83Equation 3 
Additionally, the recording-head 130 has the same speed (set movement speed Vf=Vr) during the forward and backward movements as described above. Therefore, as seen from the above equations 2, 3, the distance Dr is equal to the distance Df.
The ink drops ejected by the recording-head 130 is shot in a desired shot position Pi in the ideal state. The shot position Pi is the same position along the main scanning direction in the forward and backward movements. Therefore, as shown in FIG. 13, the recording-head 130 ejects the ink from the eject position apart from the shot position Pi by the same distance along the main scanning direction in the forward and backward movements. The ink drops 300f is ejected in the forward movement and ink drops 300r is ejected in the backward movement. When the recording-head 130 ejects the ink drops from the eject positions, the ink drops 300f and 300r are shot at the same shot position Pi in the main scanning direction. Additionally, the recording-head 130 includes a plurality of ink jet ports along the sub scanning direction. Therefore, the ink drops 300r and 300f are shot so that the drops are aligned in one row along the sub scanning direction on the recording-medium. That is, the shot ink drops (ink dots) form a line. The line by the ink dots will hereinafter be referred to as ink-dots-line.
The recording-head 130 ejects the ink drops to the respective desired shot positions Pi at constant pitches in the main scanning direction from the eject positions calculated based on the set movement speeds in the forward and backward movements. Thereby, the recording-head 130 can shoot the ink drops in the respective desired shot positions over the main scanning direction so that the ink drops are aligned in one row along the sub scanning direction. Therefore, the image-recording apparatus can shoot the ink drops in the desired positions at the constant pitches along the main scanning direction without any special control and/or processing.
However, as described above, it is very difficult to process the pulleys 111 and motor 113 without any eccentricity. The carriage-driving mechanism 110 rotates the motor 113 at a constant rotation number in order to move the carriage at the constant speed. In this case, if the pulleys 111 and motor 113 are eccentric, the movement speed of the carriage 120 fluctuates. The carriage-driving mechanism 110 is set so that the carriage 120 is constantly moved at the set movement speeds Vf, Vr. However, because of the above-described eccentricity, the carriage-driving mechanism 110 cannot convey the carriage 120 constantly at the set movement speeds Vf, Vr over the whole image-recording area ZP.
Each pulley 111 has a radius r. In this case, the speed fluctuation of the carriage 120 during the forward and backward movements is as shown in FIG. 14. FIG. 14 is a graph showing the speed fluctuation of the carriage 120, whose abscissa indicates the position of the carriage 120 in the main scanning direction and whose ordinate indicates the speed of the carriage 120.
In FIG. 14, the speed fluctuation of the carriage 120 in the forward movement is shown by a curve Cf, and the speed fluctuation in the backward movement is shown by a curve Cr. Additionally, the set movement speed Vf for the forward movement is equal to the set movement speed Vr for the backward movement. Moreover, the carriage 120 is reciprocated by driving of the pulleys 111 and motor 113. Therefore, a width of the speed fluctuation becomes the same in the forward and backward movements. Therefore, amplitudes of the speed fluctuations (widths of fluctuations of speeds with respect to the set movement speeds Vf, Vr) xcex94Vf, xcex94Vr have substantially the same value.
In the forward/backward movement, a period of the speed fluctuation of the carriage 120 is repeated every rotation of the pulleys 111. Moreover, the speed of the carriage 120 repeats increase and decrease with respect to the set movement speeds Vf, Vr in the forward/backward movement every xc2xd period of the speed fluctuation. For example, as shown in FIG. 14, in the forward movement, the movement speed of the carriage 120 is slow with respect to the set movement speed Vf during the movement from an entire position by xcfx80r. The entire position is a position where the carriage 120 enters the image-recording area ZP (position shown by 0 in FIG. 14). In other words, the movement speed of the carriage 120 is slow with respect to the set movement speed Vf between the positions 0 and xcfx80r in FIG. 14. Moreover, the movement speed of the carriage 120 is fast with respect to the set movement speed Vf from when a movement distance of the carriage 120 passes xcfx80r until the distance reaches 2xcfx80r. In other words, the movement speed of the carriage 120 is fast with respect to the set movement speed Vf between the positions xcfx80r and 2xcfx80r in FIG. 14.
Moreover, the carriage 120 is fixed to the endless belt 112. Therefore, as shown in FIG. 14, the speed fluctuation of the carriage 120 is in the same phase in the forward and backward movements. In this case, the speed becomes substantially the same in each position along the main scanning direction in the forward/backward movement. Additionally, since the recording-head 130 is attached to the carriage 120, the movement speed of the head has the same speed fluctuation as that of the carriage 120.
Therefore, as shown in FIG. 14, the movement speed of the carriage 120 is slow with respect to the set movement speed Vf between the positions 0 and xcfx80r during the backward movement similarly as during the forward movement. The speed Vf is the same as the set movement speed Vr. Therefore the movement speed of the carriage 120 is slow with respect to the speed Vr between the positions 0 and xcfx80r during the backward movement. Moreover, the movement speed of the carriage 120 is fast with respect to the set movement speed Vr between the positions xcfx80r and 2xcfx80r during the backward movement similarly as during the forward movement.
The shot positions of the ink drops ejected from the recording-head 130 which moves in a period of speed fluctuation shown in FIG. 14, will be described hereinafter with reference to FIGS. 15 and 16. FIG. 15 is a diagram showing the shot positions of the ink drops ejected by the recording-head 130 which moves at the speed fluctuation shown in FIG. 14 during the movement in a position (xc2xd)xcfx80r in FIG. 14. FIG. 16 is a diagram showing the shot positions of the ink drops ejected by the recording-head 130 which moves at the speed fluctuation shown in FIG. 14 during the movement in a position (3/2)xcfx80r in FIG. 14.
First, the shot positions of the ink drops ejected by the recording-head 130 in the position (xc2xd)xcfx80r in FIG. 14 will be described with reference to FIG. 15.
In the position (xc2xd)xcfx80r in the forward movement, as shown in FIG. 14, the movement speed of the recording-head 130 is a speed (Vfxe2x88x92xcex94Vf) obtained by subtracting xcex94Vf from the set movement speed Vf. In this case, a time for shooting the ink drops 300f onto the recording-medium 200 is similar to the time t obtained by the equation 1.
Moreover, the ink drops 300f are ejected from the recording-head 130 which is moving at the movement speed (Vfxe2x88x92xcex94Vf). Therefore, the shot positions of the ink drops 300f deviate from the shot positions Pi during the movement at the set movement speed Vf by a distance xcex94Df obtained by the following equation 4.
xcex94Df=(xe2x88x92xcex94Vf)xc3x97txe2x80x83xe2x80x83Equation 4 
That is, as shown in FIG. 15, the shot positions of the ink drops 300f deviate from the shot positions Pi by xcex94Df in a direction opposite to the moving-direction of the head.
As shown in FIG. 14, in the position (xc2xd)xcfx80r in the backward movement, the recording-head 130 has a movement speed (Vrxe2x88x92xcex94Vr) obtained by subtracting xcex94Vr from the set movement speed Vr. The time for shooting the ink drops 300r onto the recording-medium 200 is similar to the time t obtained by the equation 1.
Moreover, the ink drops 300r are ejected from the recording-head 130 which is moving at the movement speed (Vrxe2x88x92xcex94Vr). Therefore, the shot positions of the ink drops 300r deviate from the shot positions Pi during the movement at the set movement speed Vr by a distance xcex94Dr obtained by the following equation 5.
xcex94Dr=(xe2x88x92xcex94Vr)xc3x97txe2x80x83xe2x80x83Equation 5 
That is, as shown in FIG. 15, the shot positions of the ink drops 300r deviate from the shot positions Pi by xcex94Dr in the direction opposite to the moving-direction of the head.
As described above, in the position (xc2xd)xcfx80r, the ink drops 300f, 300r are apart from each other by a distance (xcex94Df+xcex94Dr) obtained by adding the distance xcex94Df to xcex94Dr along the main scanning direction.
The shot positions of the ink drops ejected by the recording-head 130 in the position (3/2)xcfx80r in FIG. 14 will next be described with reference to FIG. 16.
In the position (3/2)xcfx80r in the forward movement, as shown in FIG. 14, the movement speed of the recording-head 130 is a speed (Vf+xcex94Vf) obtained by adding xcex94Vf from the set movement speed Vf. In this case, the time for shooting the ink drops 300f onto the recording-medium 200 is similar to the time t obtained by the equation 1.
Moreover, during the forward movement, the ink drops 300f are ejected from the recording-head 130 which is moving at the movement speed (Vf+xcex94Vf). Therefore, the shot positions of the ink drops 300f deviate from the shot positions Pi during the movement at the set movement speed Vf by a distance xcex94Df obtained by the following equation 6.
xcex94Df=xcex94Vfxc3x97txe2x80x83xe2x80x83Equation 6 
That is, as shown in FIG. 16, the shot positions of the ink drops 300f deviate from the shot positions Pi by xcex94Df in the moving-direction of the head.
As shown in FIG. 14, in the position (3/2)xcfx80r in the backward movement, the recording-head 130 has a movement speed (Vr+xcex94Vr) obtained by adding xcex94Vr to the set movement speed Vr. The time for shooting the ink drops 300r onto the recording-medium 200 is similar to the time t obtained by the equation 1.
Moreover, during the backward movement the ink drops 300r are ejected from the recording-head 130 which is moving at the movement speed (Vr+xcex94Vr). Therefore, the shot positions of the ink drops 300r deviate from the shot positions Pi during the movement at the set movement speed Vr by a distance xcex94Dr obtained by the following equation 7.
xcex94Dr=xcex94Vrxc3x97txe2x80x83xe2x80x83Equation 7 
That is, as shown in FIG. 16, the shot positions of the ink drops 300r deviate from the shot positions Pi by xcex94Dr in the moving-direction of the head.
As described above, also in the position (3/2)xcfx80r, the ink drops 300f, 300r are apart from each other by the distance (xcex94Df+xcex94Dr) obtained by adding the distance xcex94Df to xcex94Dr along the main scanning direction.
When the shot positions of the ink drops 300f, 300r are apart from each other in this manner, the formed ink-dot-line spreads along the main scanning direction as compared with the ink-dot line shown in FIG. 13. That is, the width of the ink-dot-line becomes thick as compared with the ink-dot-line shown in FIG. 13.
However, in the image-recording apparatus, when the recording-head 130 ejects the ink in the position xcfx80r, similarly as the recording-head moved by the carriage-driving mechanism in the ideal state in FIG. 13, the ink drops 300f, 300r are shot in the same position along the main scanning direction. In this case, the width of the formed ink-dot-line is substantially the same as that of the ink-dot-line shown in FIG. 13.
Therefore, when the pulleys 111 and motor 113 are eccentric, for the ink-dot-lines formed in a plurality of shot positions along the main scanning direction, two types of lines narrow and wide in the main scanning direction exist in a mixed manner.
In a monochromatic image is recognized, when a ratio of dots constituting the images in one area not less than a certain size, and the other area adjacent to the one area and not less than the certain size is not less than a predetermined size, an ordinary person recognizes the presence of a gradation difference, that is, density difference in the image. This is considered in the ink dots of the image recorded in the image-recording apparatus. The ink drops 300r, 300f are shot in the predetermined positions Pi and in positions deviating from the predetermined positions Pi in a mixed manner. Therefore, in the image, the ink-dot-lines narrow and wide in the main scanning direction exist in the mixed manner. Moreover, the thin and thick ink-dot-lines are alternately and repeatedly recorded in the main scanning direction in a predetermined period. In comparison of the thin and thick ink-dot-lines with each other, there is a possibility that any person visually recognizes the presence of the density difference between the lines. In other words, the image has a difference in a spread along the main scanning direction between the adjacent ink-dot-lines. Therefore, there is a possibility that the ordinary person recognizes the presence of the density difference in the image. Therefore, there is a possibility that the image recorded by the image-recording apparatus is recognized to have a density unevenness.
In the image-recording apparatus disclosed in the Jpn. Pat. Appln. KOKAI Publication No. 1998-250058, when the pulley and motor have the eccentricity, the image-recording apparatus is will be described hereinafter.
In the image-recording apparatus described in the Jpn. Pat. Appln. KOKAI Publication No. 1998-250058, as shown in FIG. 17, a plurality of recording-heads 130 are arranged along the main scanning direction. Moreover, the recording-heads 130 are disposed apart from the adjacent recording-head 130 by a predetermined distance respectively. The predetermined distance is corresponding the movement of one period of the speed fluctuation. Therefore, these plurality of recording-heads are intend to be not influenced by the speed fluctuation by the eccentricity. In other words, each recording-head 130 is disposed apart from the adjacent recording-head 130 by the distance corresponding to the movement distance of the recording-head 130 during one rotation of the pulleys 111. Moreover, the image-recording apparatus doesn""t perform the reciprocating print mode, but a printing in a one-direction print mode.
Therefore, for each recording-head 130, the movement speed of the recording-heads 130 having ejected the ink in a position in the moving-direction of the recording-head 130 can constantly be the same as the movement speed of the adjacent recording-head 130 continuously discharging the ink in the position, respectively.
However, the image-recording apparatus described in the Jpn. Pat. Appln. KOKAI Publication No. 1998-250058, the recording-heads disposed adjacent to each other are disposed apart from each other by a distance of movement of the recording-head 130 during one rotation of the pulleys 111. Therefore, it is difficult to miniaturize the image-recording apparatus. Moreover, any solving means against the density unevenness generated in the reciprocating movement is not disclosed in the image-recording apparatus.
In consideration of the above-described problems, there has been a demand for an image-recording apparatus which reduces or prevents generation of density unevenness (color unevenness) in the recorded image and which can record a high-precision image even with the speed fluctuation of the recording-head because of the eccentricity of the pulley or the motor.
Moreover, there has been a demand for an image-recording apparatus which includes a plurality of recording-heads, which can record the high-precision image even with the speed fluctuation of the recording-head and whose main body can be miniaturized.
According to one aspect of the present invention, an image-recording apparatus conveying a recording-medium and recording an image on the recording-medium, the apparatus including a main scanning direction which crosses to the conveying direction of the recording-medium, the image-recording apparatus comprises
a recording-head discharging ink to the recording-medium;
a carriage on which the recording-head is mounted and the carriage which is reciprocatable along the main scanning direction; and
a carriage drive mechanism reciprocating the carriage along the main scanning direction,
wherein the carriage drive mechanism includes:
a pair of pulleys, a motor supplying a driving force to at least one of the pair of pulleys; and an endless belt which is extended between the pair of pulleys and on which the carriage is mounted, and
the carriage drive mechanism reciprocates the carriage so that a phase of a periodic speed fluctuation of the carriage during a forward movement of the carriage deviates from a phase of a periodic speed fluctuation of the carriage during a backward movement of the carriage.
According to another aspect of the present invention, an image-recording apparatus conveying a recording-medium and recording an image on the recording-medium, and the apparatus including a main scanning direction which crosses to the conveying direction of the recording-medium, the image-recording apparatus comprises:
the recording-head which ejects ink to the recording-medium;
a carriage on which the recording-head is mounted and the carriage which is reciprocatable along the main scanning direction; and
a carriage drive mechanism which reciprocates the carriage along the main scanning direction,
wherein the carriage drive mechanism includes:
a pair of pulleys; a motor which supplies a driving force to at least one of the pair of pulleys; and an endless belt which is extended between the pair of pulleys and on which the carriage is mounted, and
the carriage drive mechanism reciprocates the carriage and impart a phase difference of (1/X)2p radian in periodic speed fluctuation between any reciprocation and the immediately following reciprocation, where X is a number of path through which the carriage is reciprocated in a multi-pass printing mode.
According to further aspect of the present invention, an image-recording apparatus conveying a recording-medium and recording an image on the recording-medium, comprises:
a plurality of recording-heads which are arranged along a conveying direction of the recording-medium, each of the a recording-head discharging ink to the recording-medium;
a carriage on which the plurality of recording-heads are mounted and which can reciprocate along a main scanning direction crossing to a conveying direction of the recording-medium; and
a carriage drive mechanism which moves the carriage along the main scanning direction,
wherein the plurality of recording-heads are arranged so that an interval from the adjacent recording-head in the main scanning direction is a distance other than a distance integer times a distance in which carriage moves during one period of a speed fluctuation of the carriage.
According to still another aspect of the present invention, an image-recording apparatus conveying a recording-medium and recording an image on the recording-medium, the apparatus including a main scanning direction which crosses to the conveying direction of the recording-medium, the image-recording apparatus comprises:
two recording-heads which eject the same color of ink;
a carriage which holds the two recording-heads arranged along the main scanning direction and which is reciprocatable along the main scanning direction; and
a carriage drive mechanism which moves the carriage along the main scanning direction,
wherein the two recording-heads are arranged on the carriage so that an arrangement interval between the recording-heads is a distance odd-number times a distance in the carriage moves during xc2xd period of periodic speed fluctuation of the carriage,
one of the two recording-heads is used to record the image, when the carriage is moved forwards, and
the other recording-head is used to record the image, when the carriage is moved backwards.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.